HDD became very slow, help pls


I have problem with hgst touro mobile mx3 500gb.
HDD became very slow. Write speed is ok, about 80mb/s, but read is 5-15 mb/s. I have same hdd (same model 1 TB) and it works good in the same port with the same cable. I tried defragmentation, it wasnt helpful.
I tried to get support here: http://support.wdc.com/support/case2.aspx?t=hgst , but something is wrong with this form, i havent succeed to leave request.
Sorry for my english.